Design Document. DEC13-09 Chiptune Synthesizer. Wallace Davis Darren Hushak Brittany Oswald John Tuohy

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1 Design Document DEC13-09 Chiptune Synthesizer Team Members: Client: Advisor: Dustin Amesbury Wallace Davis Darren Hushak Brittany Oswald John Tuohy Dr. Joe Zambreno Dr. Nathan Neihart

2 Project Charter Version Control Version Date Author Change Description March 2013 Brittany Oswald Document created March 2013 Everyone Group collaboration via GoogleDocs to fill out most of the sections March 2013 John Tuohy Assembled and formatted the document April 2013 Brittany Oswald, Dustin Amesbury, and John Tuohy Revised and incorporated feedback

3 Table of Contents Project Charter Version Control... 2 Roles and Responsibilities... 4 Definitions and Acronyms... 5 Executive Summary... 7 Project Overview... 7 System Requirements... 7 Non Functional... 7 Functional... 8 Detailed Design... 9 User interface specification... 9 I/O Specification... 9 Hardware Specification... 9 Software Specification... 9 Simulations and Modeling... 9 Implementation Issues/Challenges... 9 Design Documents System Design Hardware Design Software Design Project References... 14

4 Roles and Responsibilities Dustin Amesbury -- Project Leader -- As the project leader, Dustin is in charge of making sure the team stays on track throughout the semester as well as leading team meetings. Dustin will also be involved with both Raspberry Pi modules. Wallace Davis -- Webmaster -- Wallace is in charge of maintaining the public website and will be involved with implementing the songbox features. Wallace will also be assisting Darren with assembling and testing the electrical components of the chipophone. Darren Hushak -- EE Director -- Darren will be the main advisor and executor of any hardware component of the project, including restoration of the organ console, its keyboards, and any of the original componentry that we wish to keep. Furthermore, Darren will be responsible for the conversion of the keyboards to MIDI controllers, addition of user input controls, and the interconnection between the MIDI controllers, the song playback and recording unit, and the sound modules. Lastly, as a music technology minor, Darren will advise and direct the group regarding standard music technology practices and music technology structures. Brittany Oswald -- User Experience Designer -- Brittany is going to ensure the finished product is able to be used by users of all skill levels and abilities. Brittany will work on retrofitting and equipping the organ with the buttons and knobs and other user interface elements. She will also participate in writing code for the sound generation and ensure a quality experience for the user. Brittany s focus will be to see the project to completion. John Tuohy -- Communications Liaison -- Along with communicating with the client and advisor, John is involved with designing and creating the software synthesizer on the Raspberry Pi.

5 Definitions and Acronyms Term Channel (MIDI) Chiptune/8-bit music Chipophone Controller (MIDI) Instrument/Voice (MIDI) MIDI Description The MIDI specification allows for 16 MIDI Channels, which are used to direct different streams of data to different destinations. Each event has a MIDI channel associated with it, and will therefore be routed based upon its channel. The broadcast channel is set per controller, and the listen channel is set per module. All MIDI channels are broadcast to every module, but it s up to the module to pick the desired channel to listen to. Chiptune music can be defined as a genre of music born out of the restrictive musical palette of 8-bit PCM audio used in the early popular gaming consoles. 8-bit refers to the bit depth of PCM audio, in that the digital form of the audio can only take on one of 2^8 values, which creates incredibly unique sounds. The unofficial name of our chiptune synthesizer A MIDI controller, most commonly a keyboard, is a device that takes user input and converts it to MIDI data. An instrument or voice is a software program or hardware component that takes MIDI data as an input and outputs either PCM or analog audio. MIDI, standing for Musical Instrument Digital Interface, is a standard for interconnection and communication between digital music devices. It is a serial protocol that only conveys events relating to musical performance, such as notes, note volume, and control values for manipulation of audio. MIDI itself does not

6 MIDI CPU Module Raspberry Pi Synthesizer convey any audio information. A MIDI CPU is a hardware circuit board that takes in analog or switched input from user interface devices (switches, potentiometers, encoders, etc), and outputs MIDI data. A MIDI module is a device that hosts an instrument/voice, which takes MIDI input and outputs audio. The module is the shell for the voice, and the voice refers to the algorithm or circuitry used to actually produce audio. Our chosen hardware platform for both our computational and signal processing needs. It is an incredibly small, yet powerful, bare-bones computer that runs a linux operating system. A synthesizer can refer to an analog or digital piece of equipment or software that can self-generate audio using various algorithms and techniques.

7 Executive Summary Our challenge is to create a device (nicknamed The Chipophone ) that will be used as a display piece for the EE/CprE department. Our chipophone is a synthesizer that plays music using chiptune or 8-bit sounds commonly associated with early console gaming systems. We are tasked with taking an existing electric organ (one which has already been donated to the project) and retrofitting it to play 8-bit music. All of the pedals, switches, and keys will be wired to create MIDI signals that will be interpreted and rendered into audio output. After the organ has been created, it will be placed in the TLA and will be used as a interactive showpiece to supplement the two arcade machines and the virtual pinball machine already located therein. Project Overview Our solution involves two stages: MIDI retrofitting the organ, and creation of an audio generation unit. We will be using MIDI CPUs to generate MIDI signals, and Raspberry Pi microcomputers to process and interpret said MIDI signals. To retrofit the organ, we will remove most of the internal mechanisms and circuitry of the organ and rewire the keyboards and button/switchboard interfaces into MIDI CPU chips. These chips will then be routed into the Raspberry Pi boards, whose audio generation code is our responsibility. The Chipophone will also allow for many features native to digital synthesizers For example, it will hold in memory various voices loadable into five different modules simultaneously; user creatable voices; mixing of multiple channels, etc. An additional third stage, to be implemented in the second semester of the project, will be to create a Songbox module, which will allow for recording and playback of both preloaded and user generated songs. System Requirements Non Functional 1 Usability a Synthesizers in general can greatly range in complexity and appear intimidating to new users. Our goal is to make our synthesizer easy to use for everyone, both advanced users who have specific goals when they play music and for a beginner user who wants to make some cool sounds. 2 Portability a The chipophone will be easily transported from event to event. It will have casters so it can be moved. The only cable will be a single power cable which plugs into a normal outlet. 3 Performance

8 a The chipophone will have no noticeable latency between keypress and sound. The chipophone will also be able to boot and be ready to play in under 30 seconds. 4 Maintainability a If anything goes wrong with any of the Raspberry Pi boards, they will be able to be easily swapped out for a new one. 5 Security a There will be a lock on the back of the chipophone, preventing anyone from stealing the boards or other equipment. Functional 1 User Controls a Keyboards and Pedals i Shall physically interact similarly to a regular organ ii Each key shall produce a sound in tune with the corresponding note played on a regular (tuned) organ b Voices i Able to change the instrument associated with each keyboard and the pedals ii Able to have the same instrument associated with more than one keyboard c Buttons and Knobs i Adjust pitch/frequency ii Adjust ADSR envelope iii Change instrument of pedals and each keyboard independently d Songbox i Selection and play default demo songs ii Pause current selection being played iii Record input iv Pause recording input v Play recorded input vi Loop recorded input 2 Technical a Use MIDI Standard b Boot time shall be less than 20 seconds, but faster is better c Instruments i There shall be 5 types of waves: two square waves with variable duty cycles, one triangle wave, one sawtooth wave, and one representing noise

9 Detailed Design User interface specification The user interface is an organ with two keyboards, a set of pedals at the feet, and a variety of control knobs near the keyboards. I/O Specification The user will interact with the keyboard keys, buttons, and pedals. These input components are all hooked up in a switching array to the MIDI CPUs. The MIDI CPUs will generate MIDI data based on what input they are getting. This MIDI data will enter the songbox Raspberry Pi through the GPIO pins on the Pi. The songbox will add any additional MIDI data required and pass on the MIDI data to the synthesizer Raspberry Pi, once again through the GPIO pins on the Pis. The MIDI data gets processed on the synthesizer and sound is produced through the 3.5mm sound jack output on the Raspberry Pi and goes to the speakers. Hardware Specification We are using two Raspberry Pi model B computer boards, four MIDI CPUs, and an existing organ that s had its internal mechanisms removed and discarded to construct The Chipophone. The organ keys, pedals, and switchboard will interface with four MIDI CPUs that produce MIDI data that gets interpreted by the Raspberry Pi boards. The whole chipophone will be powered by 5V USB. Software Specification All software will run on a distribution of Linux yet to be set in stone. Currently, it is running on the Raspbian distribution specifically made to run on the Raspberry Pi. We will be using the PortAudio library to interface with the sound drivers on the operating system. The PortMIDI library will be used to translate the UART input from the Raspberry Pi into MIDI. Simulations and Modeling For the first semester of this project, we will have a working prototype of the Chipophone. This prototype will have basic functionality with a polished look and feel. The functionality we re looking to achieve is the ability to play any note on the keyboard without any modulation. This means just basic square/triangle/noise waves. Simulating this prototype is a very simple process that can be done entirely on a computer. We re able to test the entire synthesizer in any Linux environment, which is what the Raspberry Pi is based on. Implementation Issues/Challenges Implementation of the synthesizer comes with many challenges because of a few things. The first issue is that the Raspberry Pi has an ARM based processor, meaning that code we write on our own computers likely doesn t have compilers designed to make binary executables for ARM processors.

10 Another issue we ve come across is that the Raspberry Pi and PortAudio have their own quirks about recognizing default audio devices. This has been solved by reconfiguring the library to match our device. Design Documents System Design Each of the keyboards, the pedals, and the buttons will each have their own MIDI CPU, which will take the user input and translate it to MIDI data. The songbox and the sound generation modules will each have their own dedicated Raspberry Pi, and both modules will receive MIDI data as input. As noted above, the songbox will not be implemented until next semester, but we are considering it in our design to try to mitigate the risk of trying to retrofit the module later. The audio will be generated from the parsing and sound generation module and sent through the speakers which are not pictured in the diagram above. Hardware Design The hardware for this project, on the surface, is relatively straightforward: we re using an old organ console, its two keyboards, and its pedals as the base for user input. Each keyboard must have an independent channel, and each MIDI CPU can only output one channel at a time, therefore each keyboard and the pedals will have their own CPU to encode MIDI data.

The layout of a MIDI CPU is shown below: The control terminals are what each of the switches will connect to (scheme for connections covered later) The power input is where the +5V supply connects

11 The layout of a MIDI CPU is shown below: The control terminals are what each of the switches will connect to (scheme for connections covered later) The power input is where the +5V supply connects Power access is simply a doubling of the input power pins (mainly for putting a power indicator LED in the unit) Calibration control inputs are for calibrating analog inputs, such as potentiometers. In this design, for any sort of variable (non-note) user input, we will be using encoders, so these connections will be unused Activity Indicator pins are where an LED may be placed to indicate MIDI activity on the chip; there is a built in activity monitor LED right on the chip The MIDI I/O pins are where the encoded MIDI data passes out of the MIDI CPU; the input is used only for programming the CPU; otherwise the input passes straight through the output Finally, the MIDI channel selection jumpers are used to set the MIDI channel of each CPU Because the MIDI input of each CPU is directly passed to the output, the multiple CPU s can be strung together, as shown in the following figure:

This final MIDI serial stream will then be passed into the Raspberry Pis GPIO pins.

12 The final MIDI CPU will have a serial stream of all of the MIDI data produced by the user. The MIDI spec specifically allows for this architecture, and the concatenation of multiple serial streams is handled by the CPU without any accidental bit-mixing. This final MIDI serial stream will then be passed into the Raspberry Pis GPIO pins. Finally, in order to connect each key to the MIDI CPU, we need a scheme a little more complex than a one-key-to-one-input scheme. Luckily, the MIDI CPU allows for such a scheme. By reconfiguring a few of the control pins, we can create a switching matrix, allowing for more than 23 keys to trigger MIDI events on the CPU. A small overview circuit is shown below: Between the CPU s switching matrix scheme and its ability to read encoder inputs, all of the user interface hardware is able to be handled by only 4 CPU s, all run serially together to send a single MIDI signal to the Raspberry Pi s for decoding and synthesis.

Software Design The diagram above shows a more detailed view of the software design inside the Parsing and Sound Generation module pictured in the System Design Diagram.

13 Software Design The diagram above shows a more detailed view of the software design inside the Parsing and Sound Generation module pictured in the System Design Diagram. It is important to note that the input of this module doesn t change whether the songbox is attached or not. It was designed this way on purpose to mitigate risk because the songbox will not be added until next semester. There are three main components to this design: Inputs and Change Requests, Sound Data, and Synthesis and Output. The Inputs and Change Requests component (blue box) will read the MIDI data and parse it. The MIDI standard describes sounds, but also includes program change requests, so this module will also be a decision maker and take actions based on the interpretation of the MIDI commands. Actions might include changing the qualities of the ADSR envelope for a certain module, adjusting pitch of a note, and more. This component has write access to the information in the Sound Data component. The Sound Data component keeps track of the current state of the organ. This is important because the user will be able to assign different voices or instruments to each of the

14 keyboards and the pedals, and the user will have the freedom to adjust the types of waves and qualities of the sounds resulting from the organ, and this information needs to be readily accessible and organized when creating the synthesized wave in the Synthesis and Output component. In the Synthesis and Output component, there is an audio callback which fills a buffer one element at a time based on the current Sound Data and wave properties. When this buffer is full, it is sent to the sound card, and beautiful music is made. Project References Description Linus created a similar chipophone MIDI Specification MIDI Bit Table Location

Design Document. DEC13-09 Chiptune Synthesizer. Wallace Davis Darren Hushak Brittany Oswald John Tuohy

Design Document. DEC13-09 Chiptune Synthesizer. Wallace Davis Darren Hushak Brittany Oswald John Tuohy Design Document DEC13-09 Chiptune Synthesizer Team Members: Client: Advisor: Dustin Amesbury Wallace Davis Darren Hushak Brittany Oswald John Tuohy Dr. Joe Zambreno Dr. Nathan Neihart Project Charter Version